This invention relates to novel asymmetric thioindigoid compounds which can be used to color organic materials, especially textiles.
The prior art has made little use of thioindigo derivatives as dyestuffs for synthetic organic materials, especially for polyester fibers, although many thioindigo derivatives have been used for dyeing natural fibers (for example, cotton). Recently, brilliant nuance has been desired in colored articles, especially in weaving apparel, while polyester materials colored with ordinary dyestuffs for polyester show a duller hue than the other colored synthetic organic materials (for example, polyacrylonitrile fabrics). Thus, brilliant dyestuffs for polyester materials have been sought.
This situation is also attested to by the invention of "cationic dye-dyeable polyester" that shows more brilliant hue by dyeing with cationic dyes than the hue of ordinary polyester materials dyed with ordinary dyes for polyester. On the other hand, the thioindigoid compounds show brilliant coloring effects but little dyeability for polyester materials, and therefore thioindigoid dyes for polyesters have scarcely been known except that unsubstituted thioindigo is applied only in limited uses.
The present inventors have previously discovered that certain asymmetric thioindigoid compounds can be effectively used as dyes for the coloring of organic materials, especially for polyester fibers (West Germany, OLS No. 2,401,981). The asymmetric thioindigoid compounds employed in the OLS No. 2,401,981 are good for dyeing organic materials in a wide color range of red to violet, but their dyeing properties are not necessarily satisfactory in the color range of reddish orange to red. It is desired therefore to find new asymmetric thioindigoid compounds having even better dyeing properties in a color range of reddish orange to red.
As a result of intensive colorant tests on organic materials colored with the thioindigoid compounds, it has now been discovered that the compounds of formula (I) below color synthetic organic high molecular weight compounds, especially polyester materials, in a reddish orange to red color of brilliant nuance with characteristic fluorescence. Besides, recently .alpha.-aminoanthraquinone, the most important intermediate for reddish disperse anthraquinone dyes, requires the use of a mercury catalyst in its manufacture and, as a result has caused difficult problems on environmental pollution. The new thioindigoid compounds used in this invention can be obtained without using mercury and color in more brilliant nuance than the anthraquinone derivatives.